Mummy can bake 75 cakes in 15 hours, Mummy and Sister together can bake 120 cakes in 20 hours. How many cakes Sister can bake in 30 hours?
Cakes baked by Mummy in 1 hour = $$\frac{75}{15} = 5$$
Cakes baked by Mummy and Sister together in 1 hour = $$\frac{120}{20} = 6$$
=> Cakes baked by Sister in 1 hour = 6 - 5 = 1
$$\therefore$$ Cakes baked by Sister in 30 hours = 30 $$\times$$ 1 = 30
=> Ans - (B)
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